(a) Field of the Invention
The present invention relates to a heater, and more particularly to a heater for an electronic thermostat used for cooling an engine for a vehicle and a method of manufacturing the same.
(b) Description of the Related Art
In general, an engine has a high temperature of about 2000˜2500° C. during a combustion process. At this time, a considerable amount of heat is transferred to a cylinder wall, a cylinder head, a piston valve, etc. of the engine, and therefore the strength of parts is weakened, thereby causing troubles or shortened lifespan, and generating defective combustion such as knocking or pre-ignition.
Further, if the engine is excessively cooled, heat loss is so high that the efficiency of the engine decreases and thus fuel consumption increases. Accordingly, a vehicle typically includes a thermostat to maintain a coolant temperature of the engine at about 80˜90° C.
The thermostat is installed in between the engine and a radiator, and makes displacement of a valve in accordance with variation in the coolant temperature in order to an amount of coolant flowing toward the radiator, thereby maintaining the coolant at a proper temperature.
That is, the thermostat makes the displacement of the valve so that the coolant can circulate in the radiator if the coolant temperature is equal to or higher than a setting temperature, and closes the valve so that the coolant can circulate through a bypass channel without circulating the radiator if the coolant temperature is lower than the setting temperature.
Most of conventional thermostats for a vehicle are a mechanical thermostat having a structure in which expansion force of wax expanding in proportional to the temperature of the coolant is transferred to a piston to thereby open/close the valve.
Such a mechanical thermostat simply operates to open and close the valve in accordance with the expansion of the wax under conditions of the setting temperature, and thus has a limit to positively correspond to changes in driving circumstances or other conditions of the vehicle in light of trend toward high performance and high efficiency.
Cooling performance of a vehicle has been designed taking a full load of the vehicle, but an actual load of the vehicle is not more than 70% of the full load. Therefore, the engine is super-cooled more than needs when it is actually driven, thereby decreasing fuel efficiency and deteriorating emission.
Accordingly, there is a need of control technology for maintaining an optimum coolant temperature by increasing the coolant temperature under a driving condition of a partial load, and decreasing the coolant temperature under a driving condition of the full load.
To make up for the disadvantages of the mechanical thermostat that operates based on the expansion of the wax, an electronic thermostat using a variable control method of artificially controlling the expansion of the wax has been developed and mounted to a practical vehicle.
Such an electronic thermostat controls the expansion of the wax by adjusting a heat generation rate of the heater in accordance with driving or load circumstances of the vehicle, and thus controls a flux of the coolant circulating in the radiator by adjusting an opened state of the valve, thereby variably controlling the coolant temperature and accomplishing improved fuel efficiency and stabilized emission.
However, a conventional electronic thermostat cannot control the temperature of the coolant in real time since it takes quite long time to increase the temperature of the heater to a target temperature, and cannot maximally improve the fuel efficiency of the vehicle.
For example, the conventional electronic thermostat has a structure of accommodating the wax, including a built-in heater of a film resistance type or the like, supplying electric power to the heater to generate heat, expanding the wax by heat of the heater, and pushes the piston by the expansion force, thereby operating the valve.
However, in the conventional electronic thermostat using the film resistance type heater or other heaters as described above, it takes much time (e.g., 50˜70 sec) to reach a target temperature (e.g., 300˜350° C.).
Accordingly, a heater for a thermostat is required to have a new structure capable of improving response so that time taken in increasing the heating temperature up to the target temperature can be shortened, thereby more effectively controlling the temperature of the coolant than the existing mechanical or electronic thermostat.
Further, there is a need of a heater for a thermostat, which is structurally simple, is improved in workability and productivity when manufactured and assembled, reduces production costs, and enhances durability and reliability when applied to the thermostat for controlling the temperature of the coolant.